CQ's Craig Crawford on flip-flopping at nytimes.com:

No one was more of a flip-flopper than Lincoln on the slavery question. To slavery supporters, he often spoke of the inequality of the races, implying but never explicitly saying that blacks were genetically inferior. To abolitionists, he criticized slavery but did not clearly oppose it. He successfully maintained this balancing act until emancipation became a tool to demoralize the Confederacy and win the Civil War.

William Safire on flip-flop:

In one corner of the linguistic arena, we have a heavy-hitting onomatopoeic reduplication: flip-flap, cited in the 16th century as ''they goe flip-flap in the winde,'' meaning to swing back and forth, and soon taken up by performers to describe a type of somersault, becoming flip-flop about a hundred years ago. In the opposite corner, wearing tricolor trunks, is nuance, rooted in the Latin for ''cloud'' and the French for ''shade,'' meaning ''a subtle variation in tone'' or ''delicate shading of meaning.'' According to Candy Crowley of CNN, George W. Bush once told her, ''In Texas, we don't do nuance.'' ...

To flip-flop is ''unabashedly to switch sides,'' but when done by a politician you support, it is called ''changing one's mind to comport with the nuances of new circumstances.'' A neutral term is ''to undergo a reversal of views.'' When engaged in by a politician you oppose, the verb tergiversate, pronounced with a soft g, is a choice favored by pedants, meaning ''to switch sides like an apostate.''